Radiography and Imaging
Radiography questions combine physics, technique, safety, and image interpretation. Know the difference between image types and the principles behind exposure and protection.
Core concepts
- Image types: periapical (whole tooth and apex), bitewing (crowns and interproximal bone), panoramic (broad survey), occlusal (large area of arch).
- Density and contrast: density = overall darkness; contrast = difference between light and dark areas.
- Geometric principles: the beam should be perpendicular to the film/sensor and the object; the bisecting-angle and paralleling techniques differ in how the receptor is positioned.
- ALARA: as low as reasonably achievable-use lead apron and thyroid collar, collimation, and proper exposure.
- Digital imaging reduces dose and allows instant review; sensors are more sensitive than film.
- Common errors: cone cutting, elongation (beam not perpendicular), foreshortening, overlapping contacts, and movement.
Traps
Questions often confuse elongation and foreshortening, or ask which technique reduces patient dose most (collimation and digital sensors). Another trap: assuming a panoramic image is diagnostic for caries-it is a survey tool, not a caries detector.
Rule of thumb
If the image looks stretched, the beam angle is too flat; if it looks shortened, the angle is too steep. Perpendicularity is the fix.